Colored Roofing Granules With Increased Solar Heat Reflectance, Solar Heat-Reflective Shingles, and Process For Producing Same

ABSTRACT

Solar-reflective roofing granules having deep-tone colors are formed by coating base mineral particles with a coating composition including an infrared-reflective pigment. Color is provided by colored infrared pigment, light-interference platelet pigment, or a metal oxide.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/760,299 filed Jun. 8, 2007, currently pending, which is adivision of U.S. patent application Ser. No. 10/679,898, filed Oct. 6,2003, now U.S. Pat. No. 7,241,500, issued Jul. 10, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to asphalt roofing shingles, andprotective granules for such shingles, and processes for makings suchgranules and shingles.

2. Brief Description of the Prior Art

Pigment-coated mineral rocks are commonly used as color granules inroofing applications to provide aesthetic as well as protectivefunctions to the asphalt shingles. Roofing granules are generally usedin asphalt shingle or in roofing membranes to protect asphalt fromharmful ultraviolet radiation.

Roofing granules typically comprise crushed and screened mineralmaterials, which are subsequently coated with a binder containing one ormore coloring pigments, such as suitable metal oxides. The binder can bea soluble alkaline silicate that is subsequently insolubilized by heator by chemical reaction, such as by reaction between an acidic materialand the alkaline silicate, resulting in an insoluble colored coating onthe mineral particles. Preparation of colored, coated roofing granulesis disclosed for example, in U.S. Pat. No. 2,981,636 of Lodge et al. Thegranules are then employed to provide a protective layer on asphalticroofing materials such as shingles, and to add aesthetic values to aroof.

U.S. Pat. No. 2,732,311 of Hartwright discloses a method for preparingroofing granules having metal flakes, such as aluminum flakes, adheredto their surfaces, to provide a radiation-reflective surface. Rockgranules are first mixed with kaolin clay, and then a stream of sodiumsilicate solution is added. A tacky viscous film is developed on thesurface of the granules by passing air through the mixture while it isbeing mixed, and a fine grade of metal flakes are added, and theflake-coated granules are subsequently fired to cure the clay-silicatebinder.

Pigments for roofing granules have usually been selected to provideshingles having an attractive appearance, with little thought to thethermal stresses encountered on shingled roofs. However, depending onlocation and climate, shingled roofs can experience very challengingenvironmental conditions, which tend to reduce the effective servicelife of such roofs. One significant environmental stress is the elevatedtemperature experienced by roofing shingles under sunny, summerconditions, especially roofing shingles coated with dark colored roofinggranules. Although such roofs can be coated with solar reflective paintor coating material, such as a composition containing a significantamount of titanium dioxide pigment, in order to reduce such thermalstresses, this utilitarian approach will often prove to be aestheticallyundesirable, especially for residential roofs.

Asphalt shingles coated with conventional roofing granules are known tohave low solar heat reflectance, and hence will absorb solar heatespecially through the near infrared range (700 nm-2500 nm) of the solarspectrum. This phenomenon is increased as the granules covering thesurface become dark in color. For example, while white-colored asphaltshingles can have solar reflectance in the range of 25-35%, dark-coloredasphalt shingles can only have solar reflectance of 5-15%. Furthermore,except in the white or very light colors, there is typically only a verysmall amount of pigment in the conventional granule's color coating thatreflects solar radiation well. As a result, it is common to measuretemperatures as high as 77° C. on the surface of black roofing shingleson a sunny day with 21° C. ambient temperature. Absorption of solar heatmay result in elevated temperatures at the shingle's surroundings, whichcan contribute to the so-called heat-island effects and increase thecooling load to its surroundings.

There is a continuing need for roofing materials, and especially asphaltshingles, that have improved resistance to thermal stresses whileproviding an attractive appearance. In particular, there is a need forroofing granules that provide increased solar heat reflectance to reducethe solar absorption of the shingle, while providing a wide range ofcolors including deep-tone colors to maintain the aesthetic value of thesystem.

SUMMARY OF THE INVENTION

The present invention provides roofing granules that provide increasedsolar heat reflectance, while providing deep-tone colors, as well as aprocess for preparing such roofing granules, and asphalt shingle roofingproducts incorporating such roofing granules.

In one aspect of the present invention, roofing granules are colored bythe combination of a binder, for example, a metal silicate binder orpolymeric binder suitable for outdoor exposure, and special pigmentsthat have high reflective properties towards the solar heat radiationwhile simultaneously serving as a colorant. Specifically, colored,infrared-reflective pigments, such as those disclosed in U.S. Pat. No.6,174,360 and comprising a solid solution including iron oxide, can beemployed in producing the colored infrared-reflective roofing granulesof the present invention. The colored, infrared-reflective pigment canalso comprise a near infrared-reflecting composite pigment such asdisclosed in U.S. Pat. No. 6,521,038. Composite pigments are composed ofa near-infrared non-absorbing colorant of a chromatic or black color anda white pigment coated with the near infrared-absorbing colorant.

In addition to or in the alternative to employing colored,infrared-reflective pigments selected from the group consisting of asolid solution including iron oxide and near infrared-reflectingcomposite pigments, infrared-reflective roofing granules of the presentinvention can be prepared using infrared-reflective “functional”pigments. Infrared-reflective functional pigments includelight-interference platelet pigments including titanium dioxide,light-interference platelet pigments based on metal oxidecoated-substrate, mirrorized silica pigments based upon metal-dopedsilica, and alumina. Such infrared-reflective functional pigments havebeen found to enhance the solar heat reflectance when incorporated inroofing granules.

Thus, in one aspect, the process of the present invention providesroofing granules colored by light-interference platelet pigments and/orinfrared (“IR”)-reflective color pigments to achieve higher solar heatreflection. These “pearlescent” pigments based on metal oxide-coatedsubstrates allow additional solar reflection to achieve both colors andincreased solar heat reflection. Light-interference platelet pigmentsbased on metal oxide coated-substrates are preferably selected fromthose pigments constructed from partially opaque substrates, such asmica, alumina, or silica, and metal-oxide coatings havinglight-interference properties.

In another aspect of the present invention, colored infrared-reflectiveroofing granules are provided by coating inert mineral particles with afirst coating composition including a binder and at least one reflectivewhite pigment, and curing the first coating composition on the inertmineral particles to form base particles. The base particles are thencoated with a second coating composition including a binder and at leastone colorant selected from the group consisting of uv-stabilized dyesand granule coloring pigments, and the second coating composition isthen cured. The granule coloring pigments can be conventional granulecoloring pigments based on metal oxides, or colored infrared-reflectivepigments. Optionally, the second coating composition can include atleast one infrared-reflective functional pigment.

In yet another aspect of the present invention, coloredinfrared-reflective roofing granules are provided by a processcomprising providing an inert mineral particle and coating the inertmineral particles with a first coating composition including a baseparticle binder, and at least one colorant selected from the groupconsisting of uv-stabilized dyes and granule coloring pigments, andcuring the first coating composition on the inert particles to form baseparticles. The base particles are then coated with a second coatingcomposition including a coating binder, and at least oneinfrared-reflective functional pigment selected from the groupconsisting of light-interference platelet pigments including mica,light-interference platelet pigments including titanium dioxide,mirrorized silica pigments based upon metal-doped silica, and alumina,and the second coating composition is then cured.

Coating compositions employed by the present invention can includemetal-silicate binders or organic polymeric binders. Organic bindersadvantageously permit lower curing temperatures than metal-silicatebinders, and do not require additional surface treatment for waterrepellency and staining resistance, and/or slate oils to reduce dustingduring transportation.

The process of the present invention produces coloredinfrared-reflective roofing granules that have a higher solar heatreflectance than colored roofing granules prepared using conventionalmetal oxide colorants, which typically have a solar heat reflectance offrom about 12 percent to about 20 percent. Thus, it is preferred thatthe colored infrared-reflective roofing granules of the presentinvention have a solar heat reflectance greater than about 20 percent.It is especially preferred that the colored infrared-reflective roofinggranules according to the present invention have a solar heatreflectance of at least about 25 percent, and that bituminous roofingproducts, such as asphaltic roofing shingles, made with such coloredinfrared-reflective roofing granules have a solar heat reflectance of atleast about 20 percent, more preferably at least about 25 percent, witha solar heat reflectance of at least about 30 percent being especiallypreferred.

The present invention also provides a process for increasing the solaror infrared reflectance of a colored roofing granules by at least about20 percent, more preferably at least about 25 percent, whilesubstantially maintaining the color of the roofing granules, such thatthe value of the total color difference ΔE* is no more than 10 units,more preferably no more than 5 units, and even more preferably no morethan 3 units.

In general, the process of the present invention for producing colored,infrared-reflective roofing granules comprises (a) providing baseparticles; (b) coating the base particles with a coating compositionincluding (i) a coating binder, and (ii) at least oneinfrared-reflective pigment, and (c) curing the coating composition toform coated granules. As noted above, the colored, infrared-reflectiveroofing granules of the present invention can be colored in a variety ofdifferent ways. First, the infrared-reflective pigment itself can becolored. Alternatively, the infrared-reflective pigment can be a“functional” pigment that contributes to the color of the granules, butmay be supplemented by other colorants. Finally, the color of thegranules can be supplied largely by conventional colorants, with theinfrared-reflectance being attributable to other materials.

The colored, infrared-reflective granules of the present inventionpreferably have a relatively dark shade, characterized by a value of L*of less than 85, more preferably, less than 55, and even more preferablyless than about 45.

Preferably, the coating composition comprises from about 2 percent byweight of the base particles to about 20 percent by weight of the baseparticles. More preferably, the coating composition comprises from about4 percent by weight of the base particles to about 10 percent by weightof the base particles.

In one presently preferred embodiment, the base particle binder and/orthe coating binder comprises an inorganic binder, specifically analuminosilicate material and an alkali metal silicate, and thealuminosilicate material comprises a clay. Alternatively, the baseparticle binder and/or the coating binder comprise an organic binder,such as an organic polymeric material. Preferred polymeric materialsuseful as binders include acrylic polymers and copolymers. The selectionof the binder depends upon the nature of the infrared-reflective pigmentor pigments employed, such that the binder is chosen to avoiddegradation of the pigment during cure of the binder.

It is preferred that the at least one infrared-reflective pigmentcomprises from about 1 percent by weight to about 60 percent by weightof the coating composition in which it is dispersed. When the bindercomprises an organic binder, it is especially preferred that the atleast one solar reflective pigment comprises about 40 percent by weightof the coating composition.

Preferably, in the second and third embodiments of the present process,the base particles themselves are provided by a process comprising (a)providing an inert mineral particle; (b) coating the inert mineralparticle with a base coating composition including (i) a base particlebinder, and (ii) at least one reflective white pigment, and (c) curingthe base coating composition. Optionally, the base coating compositionincludes at least one colorant. Alternatively, the base particlescomprise conventional colored roofing granules, prepared by coatinginert mineral particles with a coating composition including a silicatebinder and metal oxide pigment.

Preferably, the reflective white pigment has a solar heat reflectance ofat least about 60 percent. The reflective white pigment is preferablyselected from the group comprising titanium dioxide, zinc oxide and zincsulfide.

Preferably, the at least one reflective white pigment comprises fromabout 5 percent by weight to about 60 percent by weight of the basecoating composition (second embodiment) or first coating composition(third embodiment). More preferably, the at least one reflective whitepigment comprises from about 30 to about 40 percent by weight of thebase or first coating composition.

It is also preferred that the base or first coating compositioncomprises from about 1 percent by weight of the inert mineral particlesto about 20 percent by weight of the inert mineral particles. Morepreferably, the base or first coating composition comprises about 8percent by weight of the inert mineral particles.

The coating compositions employed in various embodiments of the processof the present invention may further comprise at least one additionalcoloring material selected from the group comprising coloring pigmentsand uv-stabilized dyes. The additional coloring material can be providedto achieve a desired color. Preferably, the coloring pigments areselected from the group comprising transition metal oxides. In addition,the coating may further comprise fillers, such as clay, talc, or glassmicrospheres, to increase the hiding of substrate.

In three presently preferred embodiments, the present invention providesa process for producing infrared-reflective roofing granules with atleast two coating layers. In these embodiments, the process includesproviding inert mineral particles and coating the inert mineralparticles with a first or base coating composition, and then curing thecured first or base coating composition to provide coated base particleshaving a first coating layer. Next, the process includes further coatingthe coated base particles with a second coating composition; and curingthe second coating composition to provide coated particles with a secondcoating layer. In two of these embodiments, the first coatingcomposition includes a base particle binder and at least oneinfrared-reflective white pigment, and the second coating compositionincludes a coating binder and a coloring material, such as a colored,infrared-reflective pigment or a colorant. In the third embodiment, thefirst coating composition includes a colorant, while the second coatingcomposition includes an infrared-reflective functional pigment.

In the second and third embodiments described above, the presentinvention provides roofing granules that have an inner coating with highsolar heat reflectance by using TiO₂ pigments or other highly reflectivepigments, and an outer coating to provide desirable colors. The innercoating is used to reflect most solar radiation that has penetrated thecolor coating in order to improve the overall solar heat reflectance.The outer color coating also optionally employs light-interferenceplatelet pigments or infrared-reflective color pigments to furtherenhance the solar heat reflectance.

In the fourth embodiment described above, the present invention providesroofing granules that have an inner color coating to provide desirablecolors and an outer coating that has infrared-reflective properties. Theouter clear coating is preferably transparent to visible light but isreflective towards the infrared range of the solar spectrum. The outercoating is comprised of suitable binders from metal-silicates or morepreferably, organic polymeric binders, and transparent IR-reflectivepigments, nano-TiO₂, or mirrorized fillers.

The infrared-reflective granules of the present invention can beprepared by pre-mixing the components of the infrared-reflectivecoating, namely the binder, pigment(s), and optional additives to aslurry consistency, followed by uniform mixing with the base particles,such as mixing in a rotary tumbler, to achieve a uniform coating on thebase particles.

The weight of the infrared-reflective coating composition is preferablyfrom about 2% by weight to about 20% of the weight of the baseparticles, more preferably from about 4% by weight to about 10% byweight of the base particles. After the mixing, the coated granules canbe dried in a rotary drum or fluidized bed with suitable heat to curethe infrared-reflective coating. Alternatively, the base particles canbe spray-coated by the pre-mixed infrared-reflective coating compositionin a rotary drum to achieve uniform coverage, followed by drying toachieve a durable infrared-reflective coating.

Preferably, an organic binder providing a high gloss appearance isemployed, to achieve added aesthetic values beyond the increase in solarheat reflectance.

The method of preparation for the infrared-reflective granules willbecome more apparent to those who are skilled in the art of coatinggranular materials with organic binders.

After the preparation of the granules to reach desirable colors,particularly in the mid to deep tone colors, the granules can then bedeposited onto the asphalt shingle surface during the shinglemanufacturing to enhance the solar heat reflectance of the finalproduct.

The present invention also provides a process for producinginfrared-reflective roofing shingles, as well as the shinglesthemselves. This process comprises producing infrared-reflective roofinggranules using the process of this invention, and adhering the granulesto a shingle stock material.

The colored, infrared-reflective roofing granules prepared according tothe process of the present invention can be employed in the manufactureof infrared-reflective roofing products, such as infrared-reflectiveasphalt shingles and roll goods, including bituminous membrane rollgoods. The colored, infrared-reflective granules of the presentinvention can be mixed with conventional roofing granules, and thegranule mixture can be embedded in the surface of bituminous roofingproducts using conventional methods. Alternatively, the colored,infrared-reflective granules of the present invention can be substitutedfor conventional roofing granules in manufacture of bituminous roofingproducts, such as asphalt roofing shingles, to provide those roofingproducts with solar-reflectance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the structure of a coloredinfrared-reflective roofing granule according to a first embodiment ofthe present invention.

FIG. 2 is a schematic illustration of the structure of a coloredinfrared-reflective roofing granule according to a second embodiment ofthe present invention.

FIG. 3 is a schematic illustration of the structure of a coloredinfrared-reflective roofing granule according to a third embodiment ofthe present invention.

FIG. 4 is a schematic illustration of the structure of a coloredinfrared-reflective roofing granule according to a fourth embodiment ofthe present invention.

FIG. 5 is a graph of solar heat reflectance versus E* (the square rootof the sum of the squares of L*, a*, and b*) for a series ofconventional inorganic pigments, a series of light-interference plateletpigment and a mixture of 65% weight/weight light-interference plateletpigment, 35% mirrorized pigment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The infrared-reflective granules of the present invention can beprepared through traditional granule coloring methods, such as thosedisclosed in U.S. Pat. No. 2,981,636, incorporated herein by reference.

Suitable inert base particles, for example, mineral particles with sizepassing #8 mesh and retaining on #70 mesh, can be coated with acombination the metal-silicate binders, kaolin clay, and reflectivepigments, or in combination of other color pigments to reach desirablecolors, followed by a heat treatment to obtain a durable coating.

Such a coating process can be repeated to form multiple coatings tofurther enhance the color and solar heat reflection.

As used in the present specification, “colored” means having an L* valueof less than 85, preferably less than 55, even more preferably less than45, when measured using a HunterLab Model Labscan XE spectrophotometerusing a 0 degree viewing angle, a 45 degree illumination angle, a 10degree standard observer, and a D-65 illuminant. “Colored” as so definedis intended to include relatively dark tones.

As used in the present specification as claims, “infrared-reflectivefunctional pigment” denotes a pigment selected from the group consistingof light-interference platelet pigments including mica,light-interference platelet pigments including titanium dioxide,mirrorized silica pigments based upon metal-doped silica, and alumina.As used in the present specification and claims, “granule coloringpigment” denotes a conventional metal oxide-type pigment employed tocolor roofing granules. UV-stabilized dyes are dye compositionsformulated with uv-stabilization materials.

As used in the present specification, the strength in color space E* isdefined as E*=(L*²+a*²+b*²)^(1/2), where L*, a*, and b* are the colormeasurements for a given sample using the 1976 CIE L*a*b* color space.The total color difference ΔE* is defined as ΔE*=(ΔL*²+Δa*²+Δb*²)^(1/2)where ΔL*, Δa*, and Δb* are respectively the differences in L*, a* andb* for two different color measurements.

The inert base particles employed in the process of the presentinvention are preferably chemically inert materials, such as inertmineral particles. The mineral particles, which can be produced by aseries of quarrying, crushing, and screening operations, are generallyintermediate between sand and gravel in size (that is, between about 8US mesh and 70 US mesh), and preferably have an average particle size offrom about 0.2 mm to about 3 mm, and more preferably from about 0.4 mmto about 2.4 mm.

In particular, suitably sized particles of naturally occurring materialssuch as talc, slag, granite, silica sand, greenstone, andesite,porphyry, marble, syenite, rhyolite, diabase, greystone, quartz, slate,trap rock, basalt, and marine shells can be used, as well as recycledmanufactured materials such as crushed bricks, concrete, porcelain, fireclay, and the like.

In one set of presently preferred embodiments, the inert base particlescomprise particles having a generally plate-like geometry. Examples ofgenerally plate-like particles include mica and flaky slate. Coloredroofing granules having a generally plate-like geometry have been foundto provide greater surface coverage when used to prepare bituminousroofing products, when compared with conventional “cubical” roofinggranules, as shown in Table 1 below. Granule surface coverage ismeasured using image analysis software, namely, Image-Pro Plus fromMedia Cybernetics, Inc., Silver Spring, Md. 20910. The shingle surfacearea is recorded in a black and white image using a CCD camera fitted toa microscope. The image is then separated into an asphalt coatingportion and a granule covering portion using the threshold method ingray scale. The amount of granule coverage is then calculated by theimage analysis software based upon the number of pixels with gray scaleabove the threshold level divided by the total number of pixels in theimage.

TABLE 1 Sample Color Granule Type Surface Coverage % A White cubical86.0 B Wood Blend cubical 86.6 C Natural flaky slate 91.6 D Naturalflaky slate 92.1 E Natural flaky slate 92.9 F Natural flaky slate 91.8

Referring now to the figures in which like reference numerals representlike element in each of the several views, there is shown in FIG. 1, aschematic illustration of the structure of a colored infrared-reflectiveroofing granule 10 according to a presently preferred first embodimentof the present invention. The colored infrared-reflective roofinggranule 10 includes a base particle 12 coated with a cured coatingcomposition 14 comprising a coating binder 16 and at least one colored,infrared-reflective pigment 18. Preferably, in the coloredinfrared-reflective roofing granules 10 the at least one colored,infrared-reflective pigment 18 is selected from the group consisting of(1) infrared-reflective pigments comprising a solid solution includingiron oxide and (2) near infrared-reflecting composite pigments.Preferably, in colored, infrared-reflective roofing granules 10, theinfrared-reflective pigment 18 comprises from about 1 percent by weightto about 60 percent by weight of the coating composition 14. Preferably,the cured coating composition 14 of the colored infrared-reflectiveroofing granules 10 further comprises at least one infrared-reflectivefunctional pigment 20 selected from the group consisting oflight-interference platelet pigments including mica, light-interferenceplatelet pigments including titanium dioxide, mirrorized silica pigmentsbased upon metal-doped silica, and alumina. Preferably, the curedcoating composition 14 comprises from about 2 percent by weight of thebase particles 12 to about 20 percent by weight of the base particles12. More preferably, the cured coating composition 14 comprises fromabout 4 percent by weight of the base particles 12 to about 10 percentby weight of the base particles 12. When alumina is included in thecoating composition 14 as an infrared-reflective functional pigment 20,the particle size of the alumina is preferably less than 425 μm. Morepreferably, the particle size of the alumina is from about 0.1 μm toabout 5 μm, and even more preferably from about 0.3 μm to about 2 μm.The coating binder 16 can comprise an aluminosilicate material, such asclay, and an alkali metal silicate. Alternatively, the coating binder 16can comprise an organic material. Optionally, the coating composition 14can include at least one coloring material selected from the groupconsisting of granule coloring pigments and uv-stabilized dyes.

Thus, in this first embodiment of colored infrared roofing granules 10of the present invention, the infrared reflectance of the coloredroofing granules 10 is attributable to the colored, infrared-reflectivepigment 18 and the optional infrared-reflective functional pigment 20,while the color of the granules 10 is substantially attributable to thecolored, infrared-reflective pigment 18.

FIG. 2 is a schematic illustration of the structure of a coloredinfrared-reflective roofing granule 30 according to a presentlypreferred second embodiment of the present invention. In thisembodiment, roofing granule 30 includes a base particle 12 comprising amineral particle 32 coated with a cured base coating composition 34including a base particle binder 36, and at least one reflective whitepigment 38. Preferably, the at least one reflective white pigment 38 isselected from the group consisting of titanium dioxide, zinc oxide andzinc sulfide. It is preferred that the at least one reflective whitepigment 38 comprises from about 5 percent by weight to about 60 percentby weight of the base coating composition 34, and more preferred thatthe at least one reflective white pigment 38 comprises from about 30percent by weight to about 40 percent by weight of the base coatingcomposition 34. In this embodiment, the base coating composition 34preferably comprises from about 1 percent by weight of the inert mineralparticles 32 to about 20 percent by weight of the inert mineralparticles 32, and more preferably, from about 4 percent by weight of thebase particles to about 10 percent by weight of the inert mineralparticles. The base particle binder 36 preferably comprises analuminosilicate material and an alkali metal silicate, and thealuminosilicate material is preferably clay, although an organicmaterial can optionally be employed as the base particle binder 36. Thecolored infrared-reflective roofing granules 30 of this secondembodiment include a second, cured coating composition 14, comprising acoating binder 14, and a colored, infrared-reflective pigment 18, aswell as an optional infrared-reflective functional pigment 20, as in thecured coating composition of the above-described first embodiment of acolored infrared-reflective roofing granule 10.

Thus, in one aspect of the present invention, a first coatingcomposition or base coating composition including a white,solar-reflective pigment such as titanium dioxide pigment is applied tothe mineral particles to cover the dark color, low infrared-reflectivemineral surface. Once the base coating is cured, a second coatingcomposition or finish coat comprising a second coating compositionincluding pigments of high infrared reflectance can then be applied andcured to create deeper tones of colors while generating a surface withhigh reflectance for solar heat.

In this second embodiment of colored infrared roofing granules 30 of thepresent invention, the infrared reflectance of the colored roofinggranules 30 is attributable to the reflective white pigment 38 in theinner layer of the cured base coating composition 34, as well as to thecolored, infrared-reflective pigment 18 and the optionalinfrared-reflective functional pigment 20 in the outer layer of thecured coating composition 14, while the color of the granules 30 issubstantially attributable to the colored, infrared-reflective pigment18 in the outer layer of the cured coating composition 14.

FIG. 3 is a schematic illustration of the structure of a coloredinfrared-reflective roofing granule 50 according to a presentlypreferred third embodiment of the present invention. In this embodiment,the colored infrared-reflective roofing granules 50 comprise baseparticles 52 comprising inert mineral particles 54 coated with a curedfirst coating composition 56 including a base particle binder 58 and atleast one reflective white pigment 60, and the base particles 52 arecoated with a cured second coating composition 62 including a coatingbinder 64, and at least one colorant 66 selected from the groupconsisting of uv-stabilized dyes and granule coloring pigments.Preferably, the cured second coating composition 62 is transparent toinfrared radiation. Preferably, the thickness of the layer formed by thecured second coating composition 62, the coating binder 64, and the atleast one colorant 66 are selected to maximize infrared transparencyconsistent with achieving the desired color tone for the roofing granule50.

Preferably, in the colored infrared-reflective roofing granules 50 theat least one colorant 66 comprises from about 1 percent by weight toabout 60 percent by weight of the second coating composition 62. In thecolored infrared-reflective roofing granules 50 of the third embodimentthe second coating composition 62 preferably further comprise at leastone infrared-reflective functional pigment 68 selected from the groupconsisting of light-interference platelet pigments including mica,light-interference platelet pigments including titanium dioxide,mirrorized silica pigments based upon metal-doped silica, and alumina,and the at least one infrared-reflective functional pigment 68preferably comprises from about 1 percent by weight to about 60 percentby weight of the second coating composition 62. When alumina is includedin the cured second coating composition 62 as an infrared-reflectivefunctional pigment 68, the particle size of the alumina is preferablyless than 425 μm. More preferably, the particle size of the alumina isfrom about 0.1 μm to about 5 μm, and even more preferably from about 0.3μm to about 2 μm. In this third embodiment, the second coatingcomposition 62 comprises from about 2 percent by weight of the baseparticles 52 to about 20 percent by weight of the base particles 52,more preferably, from about 4 percent by weight of the base particles 52to about 10 percent by weight of the base particles 52. In this thirdembodiment, the first or base coating composition 56 preferablycomprises from about 1 percent by weight of the inert mineral particles54 to about 20 percent by weight of the inert mineral particles 54. Inthis third embodiment, the base particle binder 58 preferably comprisesan aluminosilicate material and an alkali metal silicate, and thealuminosilicate material is preferably clay, although an organicmaterial can optionally be employed as the base particle binder 58.

Preferably, in this third embodiment the at least one reflective whitepigment 60 is selected from the group consisting of titanium dioxide,zinc oxide and zinc sulfide. It is preferred that the at least onereflective white pigment 60 comprises from about 5 percent by weight toabout 60 percent by weight of the base or first coating composition 56,and more preferred that the at least one reflective white pigment 60comprises from about 30 percent by weight to about 40 percent by weightof the base coating composition 56.

Thus, in this third embodiment of colored infrared-reflective roofinggranules 50 according to the present invention, the infrared reflectanceof the colored roofing granules 50 is attributable to the reflectivewhite pigment 60 in the inner layer of the cured first coatingcomposition 56, and the optional infrared-reflective functional pigment68 in the outer layer of the cured second coating composition 62, whilethe color of the granules 50 is substantially attributable to thecolorant 66 in the outer layer of the cured second coating composition62.

FIG. 4 is a schematic illustration of the structure of a coloredinfrared-reflective roofing granule 70 according to a presentlypreferred fourth embodiment of the present invention. In thisembodiment, the colored infrared-reflective roofing granule 70 comprisesinert mineral particles 74 coated with a cured first coating composition76 including a base particle binder 78 and at least one colorant 80selected from the group consisting of uv-stabilized dyes and granulecoloring pigments to form base particles 72. The base particles 72 arecoated with a cured second coating composition 84 including a coatingbinder 86 and at least one infrared-reflective functional pigment 88selected from the group consisting of light-interference plateletpigments including mica, light-interference platelet pigments includingtitanium dioxide, mirrorized silica pigments based upon metal-dopedsilica, and alumina. Optionally, the first coating composition 76further comprises at least one infrared-reflective functional pigment 82as well.

In this fourth embodiment, the at least one infrared-reflectivefunctional pigment 82 preferably comprises from about 1 percent byweight to about 60 percent by weight of the first coating composition76, as well as from about 1 percent by weight to about 60 percent byweight when the optional infrared-reflective functional pigment isemployed in the second coating composition 84. When alumina is includedin the cured first coating composition 76 or the second coatingcomposition 84 as an infrared-reflective functional pigment, theparticle size of the alumina is preferably less than 425 μm. Morepreferably, the particle size of the alumina is from about 0.1 μm toabout 5 μm, and even more preferably from about 0.3 μm to about 2 μm. Inthis fourth embodiment, the second coating composition 84 comprises fromabout 2 percent by weight of the base particles 72 to about 20 percentby weight of the base particles 72, more preferably, from about 4percent by weight of the base particles 72 to about 10 percent by weightof the base particles 72. In this fourth embodiment, the first or basecoating composition 76 preferably comprises from about 1 percent byweight of the inert mineral particles 74 to about 20 percent by weightof the inert mineral particles 74. In this fourth embodiment, the baseparticle binder 78 preferably comprises an aluminosilicate material andan alkali metal silicate, and the aluminosilicate material is preferablyclay, although an organic material can optionally be employed as thebase particle binder 78.

Thus, in this fourth embodiment of colored infrared-reflective roofinggranules 70 according to the present invention, the infrared reflectanceof the colored roofing granules 70 is attributable to theinfrared-reflective functional pigment 88 in the outer layer formed bythe cured second coating composition 84, and the optionalinfrared-reflective functional pigment 82 in the inner layer formed bythe cured first coating composition 76, while the color of the granules70 is substantially attributable to the colorant 80 in the inner layerformed by the cured first coating composition 76.

Preferably, the cured second coating composition 84 is at leastpartially transparent to infrared radiation. Preferably, the thicknessof the layer formed by the cured second coating composition 84, thecoating binder 86, and at least one infrared-reflective functionalpigment 82 are selected to maximize infrared transparency consistentwith achieving the desired color tone for the roofing granule 70.

The present invention also provides a process for increasing theinfrared or solar heat reflectance of conventional colored roofinggranules. Conventional colored roofing granules are coated with acoating composition including a coating binder and at least oneinfrared-reflective functional pigment selected from the groupconsisting of light-interference platelet pigments including mica,light-interference platelet pigments including titanium dioxide,mirrorized silica pigments based upon metal-doped silica, and alumina.In this case the infrared reflectance of the conventional coloredroofing granules is increased by at least about 20 percent, morepreferably at least about 25 percent, while substantially maintainingthe color of the roofing granules, such that the value of the totalcolor difference ΔE* is no more than 10 units, more preferably no morethan 5 units, and even more preferably no more than 3 units.

The process of the present invention for producing infrared-reflectiveroofing granules comprises several steps. In one step of the presentprocess, suitable base particles are provided. These can be suitablysized, chemically inert, mineral particles. Preferably, however, thebase particles have already been coated with an initial coatingcomposition containing a pigment, preferably a highly reflective pigmentsuch as rutile titanium dioxide. The base particles are then coatedusing a second coating composition including a binder, and at least onesolar-reflective pigment. The coating composition is then cured.Preferably, the at least one infrared-reflective functional pigment isselected from the group consisting of light-interference plateletpigments including mica, light-interference platelet pigments includingtitanium dioxide, mirrorized silica pigments based upon metal-dopedsilica, and alumina.

When alumina is employed as the at least one infrared-reflectivepigment, the alumina (aluminum oxide) preferably has a particle sizeless than #40 mesh (425 μm), preferably between 0.1 μm and 5 μm, andmore preferably between 0.3 μm and 2 μm. It is preferred that thealumina includes greater that 90 percent by weight Al₂O₃, and morepreferably, greater than 95% by weight Al₂O₃.

Preferably, the at least one infrared-reflective functional pigmentcomprises from about 1 percent by weight to about 60 percent by weightof the coating composition. It is preferred that the coating compositioncomprises from about 2 percent by weight of the base particles to about20 percent by weight of the base particles. More preferably, the coatingcomposition comprises from about 4 percent by weight of the baseparticles to about 10 percent by weight of the base particles. Thecoating composition is cured to provide a layer of solar-reflectivecoating on the base particles.

Preferably, the infrared-reflective coating is provided in a thicknesseffective to render the coating opaque to infrared radiation, such as acoating thickness of at least about 100 μm. However, advantageousproperties of the present invention can be realized with significantlylower coating thicknesses, such as at a coating thickness of from about2 μm to about 25 μm, including at a coating thickness of about 5 μm.

In one presently preferred embodiment, the base particles are preferablyprovided by a process comprising providing an inert mineral particle;coating the inert mineral particle with a base coating compositionincluding a binder and at least one colored pigment, and then curing thebase coating composition.

In another presently preferred embodiment, the base particles areprovided by a process comprising providing inert mineral particles;coating the inert mineral particles with a base coating compositionincluding a binder and at least one infrared-reflective pigment, andthen curing the base coating composition. In this case, theinfrared-reflective pigment can also be a colored pigment.

Examples of white pigments that can be employed in the process of thepresent invention include rutile titanium dioxide, anatase titaniumdioxide, lithopone, zinc sulfide, zinc oxide, lead oxide, and voidpigments such as spherical styrene/acrylic beads (Ropaque® beads, Rohmand Haas Company), and hollow glass beads having pigmentary size forincreased light scattering.

In one set of presently preferred embodiments, the colored pigmentemployed in the present invention comprises a colored,infrared-reflective pigment. Preferably, the colored,infrared-reflective pigment comprises a solid solution including ironoxide, such as disclosed in U.S. Pat. No. 6,174,360, incorporated hereinby reference. The colored infrared-reflective pigment can also comprisea near infrared-reflecting composite pigment such as disclosed in U.S.Pat. No. 6,521,038, incorporated herein by reference. Composite pigmentsare composed of a near-infrared non-absorbing colorant of a chromatic orblack color and a white pigment coated with the near infrared-absorbingcolorant. Near-infrared non-absorbing colorants that can be used in thepresent invention are organic pigments such as organic pigmentsincluding azo, anthraquinone, phthalocyanine, perinone/perylene,indigo/thioindigo, dioxazine, quinacridone, isoindolinone, isoindoline,diketopyrrolopyrrole, azomethine, and azomethine-azo functional groups.Preferred black organic pigments include organic pigments having azo,azomethine, and perylene functional groups.

Preferably, the at least one colored pigment comprises from about 0.5percent by weight to about 40 percent by weight of the base coatingcomposition. It is also preferred that base coating compositioncomprises from about 2 percent by weight of the inert mineral particlesto about 20 percent by weight of the inert mineral particles.Preferably, the base coating composition forms a layer having sufficientthickness to provide good hiding and opacity, such as a thickness offrom about 5 μm to about 50 μm.

The base particle binder and the coating binder employed in the coatingcompositions of the present invention preferably comprise analuminosilicate material, such as kaolin clay and an alkali metalsilicate, such as sodium silicate. Alternatively, the base particlebinder, and especially the coating binder, can comprise an organicmaterial, such as a curable polymeric material.

Optionally, the coating compositions of the present invention furthercomprise at least one coloring material selected from the groupconsisting of coloring pigments and uv-stabilized dyes. Presentlypreferred coloring pigments include transition metal oxides.

The coating binder employed in the process of the present invention toform the coating composition including the infrared-reflective pigmentis preferably formed from a mixture of an alkali metal silicate, such asaqueous sodium silicate, and heat reactive aluminosilicate material,such as clay, preferably, kaolin. The proportion of alkali metalsilicate to heat-reactive aluminosilicate material is preferably fromabout 3:1 to about 1:3 parts by weight alkali metal silicate to parts byweight heat-reactive aluminosilicate material, more preferably about 2:1to about 0.8:1 parts by weight alkali metal silicate to parts by weightheat-reactive aluminosilicate material. Alternatively, the base granulescan be first mixed with the heat reactive aluminosilicate to coat thebase granules, and the alkali metal silicate can be subsequently addedwith mixing.

The base particle binder employed in the base coating composition cansimilarly be formed from a mixture of an alkali metal silicate, such asaqueous sodium silicate, and heat reactive aluminosilicate material,such as clay, preferably, kaolin. The base coating binder can be thesame as that employed for the solar-reflective coating.

When the infrared-reflective granules are fired at an elevatedtemperature, such as at least about 200 degrees C., and preferably about250 to 500 degrees C., the clay reacts with and neutralizes the alkalimetal silicate, thereby insolubilizing the binder. The binder resultingfrom this clay-silicate process, believed to be a sodium aluminumsilicate, is porous, such as disclosed in U.S. Pat. No. 2,379,358(incorporated herein by reference). Alternatively, the porosity of theinsolubilized binder can be decreased by including an oxygen containingboron compound such as borax in the binder mixture, and firing thegranules at a lower temperature, for example, about 250 degree C. to 400degrees C., such as disclosed in U.S. Pat. No. 3,255,031 (incorporatedherein by reference).

Examples of clays that can be employed in the process of the presentinvention include kaolin, other aluminosilicate clays, Dover clay,bentonite clay, etc.

The inorganic binder employed in the present invention can include analkali metal silicate such as an aqueous sodium silicate solution, forexample, an aqueous sodium silicate solution having a total solidscontent of from about 38 percent by weight to about 42 percent byweight, and having a ratio of Na₂O to SiO₂ of from about 1:2 to about1:3.25.

Organic binders can also be employed in the process of the presentinvention. The use of suitable organic binders, when cured, can alsoprovide superior granule surface with enhanced granule adhesion to theasphalt substrate and with better staining resistance to asphalticmaterials. Roofing granules colored by inorganic binders often requireadditional surface treatments to impart certain water repellency forgranule adhesion and staining resistance. U.S. Pat. No. 5,240,760discloses examples of polysiloxane-treated roofing granules that provideenhanced water repellency and staining resistance. With the organicbinders, the additional surface treatments may be eliminated. Also,certain organic binders, particularly those water-based systems, can becured by drying at much lower temperatures as compared to the inorganicbinders such as metal-silicates, which often require curing attemperatures greater than about 500° C. or by using a separate picklingprocess to render the coating durable.

Examples of organic binders that can be employed in the process of thepresent invention include acrylic polymers, alkyd and polyesters, aminoresins, epoxy resins, phenolics, polyamides, polyurethanes, siliconeresins, vinyl resins, polyols, cycloaliphatic epoxides, polysulfides,phenoxy, fluoropolymer resins. Examples of uv-curable organic bindersthat can be employed in the process of the present invention includeuv-curable acrylates and uv-curable cycloaliphatic epoxides.

An organic material can be employed as a binder for the coatingcomposition used in the process of the present invention. Preferably, ahard, transparent organic material is employed. Especially preferred areuv-resistant polymeric materials, such as poly(meth)acrylate materials,including poly methyl methacrylate, copolymers of methyl methacrylateand alkyl acrylates such as ethyl acrylate and butyl acrylate, andcopolymers of acrylate and methacrylate monomers with other monomers,such as styrene. Preferably, the monomer composition of the copolymer isselected to provide a hard, durable coating. If desired, the monomermixture can include functional monomers to provide desirable properties,such as crosslinkability to the copolymers. The organic material can bedispersed or dissolved in a suitable solvent, such as coatings solventswell known in the coatings arts, and the resulting solution used to coatthe granules using conventional coatings techniques. Alternatively,water-borne emulsified organic materials, such as acrylate emulsionpolymers, can be employed to coat the granules, and the watersubsequently removed to allow the emulsified organic materials of thecoating composition to coalesce.

Examples of near IR-reflective pigments available from the ShepherdColor Company, Cincinnati, Ohio, include Arctic Black 10C909 (chromiumgreen-black), Black 411 (chromium iron oxide), Brown 12 (zinc ironchromite), Brown 8 (iron titanium brown spinel), and Yellow 193 (chromeantimony titanium).

Light-interference platelet pigments are known to give rise to variousoptical effects when incorporated in coatings, including opalescence or“pearlescence.” Surprisingly, light-interference platelet pigments havebeen found to provide or enhance infrared-reflectance of roofinggranules coated with compositions including such pigments.

Examples of light-interference platelet pigments that can be employed inthe process of the present invention include pigments available fromWenzhou Pearlescent Pigments Co., Ltd., No. 9 Small East District,Wenzhou Economical and Technical Development Zone, Peoples Republic ofChina, such as Taizhu TZ5013 (mica, rutile titanium dioxide and ironoxide, golden color), TZ5012 (mica, rutile titanium dioxide and ironoxide, golden color), TZ4013 (mica and iron oxide, wine red color),TZ4012 (mica and iron oxide, red brown color), TZ4011 (mica and ironoxide, bronze color), TZ2015 (mica and rutile titanium dioxide,interference green color), TZ2014 (mica and rutile titanium dioxide,interference blue color), TZ2013 (mica and rutile titanium dioxide,interference violet color), TZ2012 (mica and rutile titanium dioxide,interference red color), TZ2011 (mica and rutile titanium dioxide,interference golden color), TZ1222 (mica and rutile titanium dioxide,silver white color), TZ1004 (mica and anatase titanium dioxide, silverwhite color), TZ4001/600 (mica and iron oxide, bronze appearance),TZ5003/600 (mica, titanium oxide and iron oxide, gold appearance),TZ1001/80 (mica and titanium dioxide, off-white appearance), TZ2001/600(mica, titanium dioxide, tin oxide, off-white/gold appearance),TZ2004/600 (mica, titanium dioxide, tin oxide, off-white/blueappearance), TZ2005/600 (mica, titanium dioxide, tin oxide,off-white/green appearance), and TZ4002/600 (mica and iron oxide, bronzeappearance).

Examples of light-interference platelet pigments that can be employed inthe process of the present invention also include pigments availablefrom Merck KGaA, Darmstadt, Germany, such as Iriodin® pearlescentpigment based on mica covered with a thin layer of titanium dioxideand/or iron oxide; Xirallic™ high chroma crystal effect pigment basedupon Al₂O₃ platelets coated with metal oxides, including Xirallic T60-10 WNT crystal silver, Xirallic T 60-20 WNT sunbeam gold, andXirallic F 60-50 WNT fireside copper; Color Stream™ multi color effectpigments based on SiO₂ platelets coated with metal oxides, includingColor Stream F 20-00 WNT autumn mystery and Color Stream F 20-07 WNTviola fantasy; and ultra interference pigments based on TiO₂ and mica.

Examples of mirrorized silica pigments that can be employed in theprocess of the present invention include pigments such as Chrom Brite™CB4500, available from Bead Brite, 400 Oser Ave, Suite 600, Hauppauge,N.Y. 11788.

Aluminum oxide, preferably in powdered form, can be used assolar-reflective additive in the color coating formulation to improvethe solar reflectance of colored roofing granules without affecting thecolor. The aluminum oxide should have particle size less than #40 mesh(425 μm), preferably between 0.1 μm and 5 μm. More preferably, theparticle size is between 0.3 μm and 2 μm. The alumina should havepercentage Al₂O₃>90%, more preferably >95%.

The infrared-reflective roofing granules of the present invention caninclude conventional coatings pigments. Examples of coatings pigmentsthat can be used include those provided by the Color Division of FerroCorporation, 4150 East 56th St., Cleveland, Ohio 44101, and producedusing high temperature calcinations, including PC-9415 Yellow, PC-9416Yellow, PC-9158 Autumn Gold, PC-9189 Bright Golden Yellow, V-9186Iron-Free Chestnut Brown, V-780 Black, V0797 IR Black, V-9248 Blue,PC-9250 Bright Blue, PC-5686 Turquoise, V-13810 Red, V-12600 CamouflageGreen, V12560 IR Green, V-778 IR Black, and V-799 Black. Furtherexamples of coatings pigments that can be used include white titaniumdioxide pigments provided by Du Pont de Nemours, P.O. Box 8070,Wilmington, Del. 19880.

Pigments with high near IR transparency are preferred for use incoatings applied over white, reflective base coats. Such pigmentsinclude pearlescent pigments, light-interference platelet pigments,ultramarine blue, ultramarine purple, cobalt chromite blue, cobaltaluminum blue, chrome titanate, nickel titanate, cadmium sulfide yellow,cadmium sulfoselenide orange, and organic pigments such as phthalo blue,phthalo green, quinacridone red, diarylide yellow, and dioxazine purple.Conversely, color pigments with significant infrared absorbency and/orlow infrared transparency are preferably avoided when preparing coatingsfor use over white, reflective base coats. Examples of pigmentsproviding high infrared absorbency and/or low infrared transparencyinclude carbon black, iron oxide black, copper chromite black, ironoxide brown natural, and Prussian blue.

The solar heat reflectance properties of the solar heat-reflectiveroofing granules of the present invention are determined by a number offactors, including the type and concentration of the solarheat-reflective pigment(s) used in the solar heat-reflective coatingcomposition, whether a base coating is employed, and if so, the type andconcentration of the reflective white pigment employed in the basecoating, the nature of the binder(s) used in for the solarheat-reflective coating and the base coating, the number of coats ofsolar heat-reflective coating employed, the thickness of the solarheat-reflective coating layer and the base coating layer, and the sizeand shape of the base particles.

Infrared-reflective coating compositions according to the presentinvention can also include supplementary pigments to spaceinfrared-reflecting pigments, to reduce absorption bymultiple-reflection. Examples of such “spacing” pigments includeamorphous silicic acid having a high surface area and produced by flamehydrolysis or precipitation, such as Aerosil TT600 supplied by Degussa,as disclosed in U.S. Pat. No. 5,962,143, incorporated herein byreference.

The present invention provides mineral surfaced asphalt shingles with L*less than 85, and more preferably less than 55, and solar reflectancegreater than 25%. Preferably, asphalt shingles according to the presentinvention comprise colored, infrared-reflective granules according tothe present invention, and optionally, conventional colored roofinggranules. Conventional colored roofing granules and infrared-reflectiveroofing granules can be blended in combinations to generate desirablecolors. The blend of granules is then directly applied on to hot asphaltcoating to form the shingle. Examples of granule deposition apparatusthat can be employed to manufacture asphalt shingles according to thepresent invention are provided, for example, in U.S. Pat. Nos.4,583,486, 5,795,389, and 6,610,147, and U.S. Patent ApplicationPublication U.S. 2002/0092596.

The process of the present invention advantageously permits the solarreflectance of the shingles employing the solar-reflective granules tobe tailored to achieve specific color effects.

The colored, infrared-reflective granules prepared according to theprocess of the present invention can be employed in the manufacture ofinfrared-reflective roofing products, such as infrared-reflectiveasphalt shingles, using conventional roofing production processes.Typically, bituminous roofing products are sheet goods that include anon-woven base or scrim formed of a fibrous material, such as a glassfiber scrim. The base is coated with one or more layers of a bituminousmaterial such as asphalt to provide water and weather resistance to theroofing product. One side of the roofing product is typically coatedwith mineral granules to provide durability, reflect heat and solarradiation, and to protect the bituminous binder from environmentaldegradation. The colored, infrared-reflective granules of the presentinvention can be mixed with conventional roofing granules, and thegranule mixture can be embedded in the surface of such bituminousroofing products using conventional methods. Alternatively, the colored,infrared-reflective granules of the present invention can be substitutedfor conventional roofing granules in manufacture of bituminous roofingproducts to provide those roofing products with solar reflectance.

Bituminous roofing products are typically manufactured in continuousprocesses in which a continuous substrate sheet of a fibrous materialsuch as a continuous felt sheet or glass fiber mat is immersed in a bathof hot, fluid bituminous coating material so that the bituminousmaterial saturates the substrate sheet and coats at least one side ofthe substrate. The reverse side of the substrate sheet can be coatedwith an anti-stick material such as a suitable mineral powder or a finesand. Roofing granules are then distributed over selected portions ofthe top of the sheet, and the bituminous material serves as an adhesiveto bind the roofing granules to the sheet when the bituminous materialhas cooled. The sheet can then be cut into conventional shingle sizesand shapes (such as one foot by three feet rectangles), slots can be cutin the shingles to provide a plurality of “tabs” for ease ofinstallation, additional bituminous adhesive can be applied in strategiclocations and covered with release paper to provide for securingsuccessive courses of shingles during roof installation, and thefinished shingles can be packaged. More complex methods of shingleconstruction can also be employed, such as building up multiple layersof sheet in selected portions of the shingle to provide an enhancedvisual appearance, or to simulate other types of roofing products.Alternatively, the sheet can be formed into membranes or roll goods forcommercial or industrial roofing applications.

The bituminous material used in manufacturing roofing products accordingto the present invention is derived from a petroleum-processingby-product such as pitch, “straight-run” bitumen, or “blown” bitumen.The bituminous material can be modified with extender materials such asoils, petroleum extracts, and/or petroleum residues. The bituminousmaterial can include various modifying ingredients such as polymericmaterials, such as SBS (styrene-butadiene-styrene) block copolymers,resins, flame-retardant materials, oils, stabilizing materials,anti-static compounds, and the like. Preferably, the total amount byweight of such modifying ingredients is not more than about 15 percentof the total weight of the bituminous material. The bituminous materialcan also include amorphous polyolefins, up to about 25 percent byweight. Examples of suitable amorphous polyolefins include atacticpolypropylene, ethylene-propylene rubber, etc. Preferably, the amorphouspolyolefins employed have a softening point of from about 130 degrees C.to about 160 degrees C. The bituminous composition can also include asuitable filler, such as calcium carbonate, talc, carbon black, stonedust, or fly ash, preferably in an amount from about 10 percent to 70percent by weight of the bituminous composite material.

The following examples are provided to better disclose and teachprocesses and compositions of the present invention. They are forillustrative purposes only, and it must be acknowledged that minorvariations and changes can be made without materially affecting thespirit and scope of the invention as recited in the claims that follow.

In the examples, granule color measurements were made using the RoofingGranules Color Measurement Procedure from the Asphalt RoofingManufacturers Association (ARMA) Granule Test Procedures Manual, ARMAForm No. 441-REG-96.

Example 1

Roofing granules are prepared by using 1 kg of US #11 grade mineralparticles as a base followed by color coating with a mixture of 35 gsodium silicate binder from Occidental Petroleum Corp., 17.5 g of kaolinclay from Unimin Corp., and 16 g of TZ1001 pearlescent pigment fromGlobal Pigments, LLC. The color-coated granules are heat-treated in arotary drum at temperatures between 480° C.-510 C.° in order to cure thecoating. The finished granules have a brownish gray appearance with anaverage solar heat reflectance of 23.5% measured by a D&S SolarReflectometer, as compared to initial solar reflectance of 18.2%.

Example 2

In this example, a highly reflective, white-pigmented inner coating isused as a substrate to reflect additional infrared radiation, while anouter color coating with IR-reflective pigments are used to providedesirable colors. 1 kg of white TiO₂ pigmented roofing granules withsolar heat reflectance greater than 30% (CertainTeed Corp., Gads Hill,Mo.) are used as the base mineral particles and are colored by a secondcoating comprised of 100 g organic binder (Rohm and Haas Rhoplex®EI-2000), 12 g of TZ4002 and 3 g of TZ1003 pearlescent pigments bothfrom Global Pigments, LLC. The resultant granules are dried in afluidized bed dryer to a free-flowing granular mass with very desirabledeep, reddish gold appearance (L*=44.10, a*=20.79, b*=18.59). The curedgranule sample has a high solar reflectance of 31.0% as compared to the22% reflectance of roofing granules with similar colors obtained bytypical inorganic pigments, e.g., Bayer 3488x tan (CI #77496) pigmentand the Bayer 120N red (CI #77491) pigment.

Examples 3a, 3b and 3c

The effects of light-interference platelet pigments on solar heatreflectance is evaluated by a drawdown method. Samples of drawdownmaterial are prepared by mixing 20 g of sodium silicate from OccidentalPetroleum Corp. and 2 g of each of TZ5013, TZ5012, TZ4013 pearlescentpigments from Global Pigments, LLC, respectively, using a mechanicalstirrer under low shear conditions. Each coating is cast from arespective sample of drawdown material using a 10 mil stainless steeldrawdown bar (BYK-Gardner, Columbia, Md.) on a WB chart from LenetaCompany. The resulting uniform coating is air-dried to touch and thesolar heat reflectance is measured using a D&S Solar Reflectometer. Thecolor is also measured using a HunterLab Colorimeter. By plotting thesolar heat reflectance vs. the strength in color space using E*(E*=(L*²+a*²+b*²)^(1/2), it is shown that the light-interferenceplatelet pigments exhibit significantly higher solar heat reflectanceover the traditional inorganic color pigments, e.g., iron-oxide redpigments (120N from Bayer Corp.; R-4098 from Elementis Corp.),ultramarine blue pigment (5007 from Whittaker), mixed metal-oxide yellowpigments (3488x from Bayer Corp.; 15A from Rockwood Pigments),chrome-oxide green pigments (GN from Bayer Corp.), or iron-oxide umberpigments (JC444 from Davis Colors), while creating a deep, desirabletan, gold, or purplish red colors. The results of the measurements areprovided below in Table 2 and displayed in FIG. 5.

Examples 4a and 4b

The effect of employing a mirrorized pigment on solar heat reflectanceis demonstrated by using the drawdown method of Example 3. The test isrepeated except that mirrorized pigments from Bead Brite Glass Products,Inc. are substituted for 20% by weight of the pearlescent pigments ofExamples 3b and 3c. The results, which show further enhancement of solarheat reflectance, are provided in Table 2 and displayed in FIG. 5.

TABLE 2 Solar heat Pigment Type Color Reading, E* reflectanceComparative Bayer 120N Red 53.88 0.332 Example 1 Comparative Whittaker5007 76.17 0.298 Example 2 Ultramarine Blue Comparative Elementis R4098Red 48.47 0.320 Example 3 Iron Oxide Comparative Davis Colors JC 44414.44 0.077 Example 4 Umber Comparative Rockwood 15A Tan 71.93 0.385Example 5 Comparative Bayer GN Chrome 46.46 0.313 Example 6 Oxide GreenComparative Bayer 3488x Tan 70.54 0.339 Example 7 Example 3a GlobalPigments TZ 91.82 0.653 5013 Tan Example 3b Global Pigments TZ 77.060.539 5012 Gold Example 3c Global Pigments 53.66 0.431 TZ4013 RedExample 4a 65% TZ 5012 + 20% 81.74 0.560 Mirrorized Pigment Example 4b65% TZ 4013 + 20% 57.15 0.446 Mirrorized Pigment

Example 5

Roofing granules are prepared by using 1 kg of US #11 grade mineralparticles as a base followed by color coating with a mixture of 40.6 gsodium silicate binder from Occidental Petroleum Corp., 25.0 g of kaolinclay from Wilky Clay Co., 2.6 g of 799 black pigment from Ferro Corp.,and 2.5 g of 9508SW pearlescent pigment from EM Industries Inc. Thecolor-coated granules are heat-treated in a rotary drum at elevatedtemperature between 480° C.-510° C. in order to cure the coating. Thefinished granules have a color reading of L*=32.77, a*=5.05, b*=5.66 asmeasured by the HunterLab colorimeter, and match closely to acommercially available roofing granules of #41 brown from CertainTeedCorp., Norwood, Mass. The prepared granules with IR-pigments have asolar heat reflectance of 22%, which is significantly higher than the14% solar heat reflectance obtained from the #41 brown roofing granulesmade from non-IR pigments, e.g., the Bayer 3488x tan (CI #77496)pigment, the Bayer 120N red (CI #77491) pigment, the 807 carbon black(CI #77266) from Rockwood Pigments, and the JC444 umber pigment (CI#77499) also from Rockwood Pigments Co.

Example 6

The effect of transparent, IR-reflective pigments based on metaloxide-mica is demonstrated by using the drawdown method of Example 3.20g of sodium silicate binder (Occidental Petroleum Corp.) and 0.1 g ofthe said pigment (Solar Flair 870, EM Industries, Inc., Hawthorne, N.Y.)are mixed at 300 rpm using a mechanical stirrer under low shearconditions and are drawn to form a thin, clear coating with 10 mildrawdown application (BYK-Gardner, Columbia, Md.) on a black lacqueredpaper (Leneta 5C, also from BYK-Gardner, Columbia, Md.). Afterair-drying, the solar reflectance of the clear coating is measured usinga D&S Solar Reflectometer against the black background. The coating isfound to increase the solar heat reflectance from 7.8% of the blackbackground to 10.7%, without any visible change to the background color.

Example 7

A coating formulation for roofing granules comprising of 32.5 g sodiumsilicate (Oxychem grade 42), 20.1 g of kaolin slurry (Royale slurry fromUnimin Corp.), and 3.6 g of water was prepared in a container by mixingthe ingredients using a mechanical stirrer at 300 rpm under low shearconditions. The coating composition had an off-white color and wasevaluated by drawdown method using a 10 mil drawdown bar (#SAR-5306 fromBYK Gardner Instruments) on a drawdown paper (Form 105C from LenetaCo.). The coating had a color reading of L*=86.53, a*=0.41, andb*=16.24, as measured using a HunterLab calorimeter, and a solarreflectance of 15% as measured by a portable solar reflectometer (Device& Service Instrument) against a black background. 2.0 g of aluminapowder with a particle size of 0.3 mm (Op-Alumina powder from Struers)was added to the same coating formulation. The resulting coatingcomposition was evaluated by using the same drawdown method. Theaddition of alumina powder was found to significantly increase thecoating solar reflectance to 24%, while keeping the color reading aboutthe same at L*=86.25, a*=0.56, and b*=16.04.

Various modifications can be made in the details of the variousembodiments of the processes, compositions and articles of the presentinvention, all within the scope and spirit of the invention and definedby the appended claims.

1. Colored infrared-reflective roofing granules comprising baseparticles comprising inert mineral particles coated with a cured firstcoating composition including a base particle binder and at least onereflective white pigment, the base particles being coated with a curedsecond coating composition including a coating binder, and at least onecolorant selected from the group consisting of pigments with high nearinfrared transparency.
 2. Colored infrared-reflective roofing granulesaccording to claim 1 wherein the at least colorant is selected from thegroup consisting of pearlescent pigments, light-interference plateletpigments, ultramarine blue, ultramarine purple, cobalt chromite blue,cobalt aluminum blue, chrome titanate, nickel titanate, cadmium sulfideyellow, cadmium sulfoselenide orange, and organic pigments selected fromthe group consisting of phthalo blue, phthalo green, quinacridone red,diarylide yellow, and dioxazine purple.
 3. Colored infrared reflectiveroofing granules according to claim 1 wherein the at least one colorantis selected from the group consisting of metal oxide pigments. 4.Colored infrared-reflective roofing granules according to claim 1wherein the at least colorant is selected from the group consisting ofPC-9415 Yellow, PC-9416 Yellow, PC-9158 Autumn Gold, PC-9189 BrightGolden Yellow, V-9186 Iron-Free Chestnut Brown, V-780 Black, V0797 IRBlack, V-9248 Blue, PC-9250 Bright Blue, PC-5686 Turquoise, V-13810 Red,V-12600 Camouflage Green, V12560 IR Green, V-778 IR Black, and V-799Black.
 5. Colored infrared-reflective roofing granules according toclaim 1 wherein the at least one reflective white pigment is selectedfrom the group consisting of titanium dioxide, zinc oxide and zincsulfide.
 6. Colored infrared-reflective roofing granules according toclaim 1, the colored infrared-reflective roofing granules having an L*value of less than
 55. 7. Colored infrared-reflective roofing granulesaccording to claim 1 the colored infrared-reflective roofing granuleshaving an infrared reflectance of at least 25%.
 8. A bituminous roofingproduct comprising a substrate sheet of a fibrous material saturatedwith a bituminous coating material and colored infrared-reflectiveroofing granules comprising base particles comprising inert mineralparticles coated with a cured first coating composition including a baseparticle binder and at least one reflective white pigment, the baseparticles being coated with a cured second coating composition includinga coating binder, and at least colorant selected from the groupconsisting of pigments with high near infrared transparency.
 9. Abituminous roofing product according to claim 8 having an L* value ofless than
 55. 10. A bituminous roofing product according to claim 8having an infrared reflectance of at least 25%.
 11. A bituminous roofingproduct according to claim 8 wherein the at least colorant is selectedfrom the group consisting of pearlescent pigments, light-interferenceplatelet pigments, ultramarine blue, ultramarine purple, cobalt chromiteblue, cobalt aluminum blue, chrome titanate, nickel titanate, cadmiumsulfide yellow, cadmium sulfoselenide orange, and organic pigmentsselected from the group consisting of phthalo blue, phthalo green,quinacridone red, diarylide yellow, and dioxazine purple.
 12. Abituminous roofing product according to claim 8 wherein the at least onecolorant is selected from the group consisting of metal oxide pigments.13. A bituminous roofing product according to claim 8 wherein the atleast colorant is selected from the group consisting of PC-9415 Yellow,PC-9416 Yellow, PC-9158 Autumn Gold, PC-9189 Bright Golden Yellow,V-9186 Iron-Free Chestnut Brown, V-780 Black, V0797 IR Black, V-9248Blue, PC-9250 Bright Blue, PC-5686 Turquoise, V-13810 Red, V-12600Camouflage Green, V12560 IR Green, V-778 IR Black, and V-799 Black. 14.A bituminous roofing product according to claim 8 wherein the baseparticles comprise mineral particles coated with a cured base coatingcomposition including a base coating binder and at least one reflectivewhite pigment.
 15. A bituminous roofing product according to claim 8wherein the at least one reflective white pigment is selected from thegroup consisting of titanium dioxide, zinc oxide and zinc sulfide.
 16. Abituminous roofing product according to claim 8 having an L* value ofless than
 55. 17. A bituminous roofing product according to claim 8having an infrared reflectance of at least 25%.